What is Diquat* and Why Does It Matter?

Diquat is a fast-acting herbicide used to kill weeds and aquatic plants. Farmers apply it to crops like potatoes, sugarcane, and soybeans. It's also widely used to clear vegetation from ponds, irrigation canals, and drainage ditches. After application, diquat can wash into nearby streams, rivers, and groundwater — eventually reaching the water systems that supply your tap.

Once diquat enters a water supply, it doesn't break down quickly. It binds to soil particles and sediment, which means runoff events after rain can carry it long distances. Agricultural areas with heavy herbicide use are especially vulnerable. The chemical is water-soluble enough to slip through standard water treatment processes that weren't designed to target pesticides.

The EPA sets a maximum contaminant level (MCL) for diquat at 20 parts per billion (ppb) in drinking water. The good news is that none of the 19 water systems where diquat was detected exceeded that legal limit. The average detected level was 0.236 ppb, with the highest reading coming in at 0.722 ppb — well below the EPA threshold. However, the EPA's legal limits aren't always the same as what's considered safe for long-term daily exposure. The Environmental Working Group (EWG) points out that the EPA's diquat standard hasn't been updated to reflect current health research. Long-term exposure to diquat — even at low levels — has been linked to cataracts and kidney and liver damage in animal studies (EPA). At high doses, it can cause serious neurological harm. The research on low-level chronic exposure in humans is still developing, which is exactly why some health advocates argue for more conservative guidelines.

The geographic pattern here tells a clear story. Texas accounts for 13 of the 19 systems where diquat was detected — more than two-thirds of all reported cases. Louisiana and Kentucky each show 2 detections, with Florida and Maine rounding out the list with 1 each. That Texas dominance makes sense. The state has millions of acres of row crops, including cotton and sorghum, where diquat is commonly applied. It also has an extensive network of irrigation canals that can carry herbicide residue directly toward water intakes. Louisiana's detections likely tie to its sugarcane farming regions, where diquat is a standard tool for pre-harvest desiccation — a process that dries out the crop before cutting. Kentucky's agricultural mix, including tobacco and grain crops, creates similar runoff risks.

So what can you actually do about it? Activated carbon filtration is a solid first line of defense against diquat. Standard pitcher filters with carbon blocks can reduce diquat levels meaningfully. But if you want the most thorough protection, a reverse osmosis (RO) system is your best option. Reverse osmosis forces water through a semipermeable membrane that blocks contaminants at the molecular level, removing up to 99% of pesticides and herbicides including diquat. Echo Water's reverse osmosis systems are designed specifically for this kind of whole-home or under-sink protection. They're built to handle the full range of agricultural contaminants that standard municipal treatment can miss.

If you live in Texas, Louisiana, or Kentucky — especially in a rural or semi-rural area near farmland — it's worth knowing your water source and asking your utility for its most recent water quality report. You can also request independent testing if you want a clearer picture of what's actually coming out of your tap. Diquat levels in these systems are currently below legal limits, but "legal" and "risk-free" aren't always the same thing. Taking a proactive step now, like adding a quality filtration system, means you're not waiting for the science to catch up before protecting your family.

Regulatory Standards for Diquat*

Cities With the Highest Diquat* Levels

States Most Affected by Diquat*

Frequently Asked Questions

Related Contaminant Guides